The present invention relates to a method and apparatus for recording graphic or image information by means of punctiform recording spots that are arranged line-by-line according to a recording grid, or multi-lined within a matrix, and the recording effected step by step, with a recording frequency corresponding to the point intervals or pitch of the grid or matrix, and in which at the beginning of a contour proceeding obliquely to the recording direction the first recording spot is displaced in the direction of the contour by at least a fractional pitch step when its edge does not coincide with the contour, and recording the following recording spots step-by-step in the pulse of the recording frequency.
Recording methods are known in which the image or graphic characters are recorded by the formation of covered surfaces arranged in a grid, for example mosaic printers, which operate with needles, thermographic or electric recording combs. Ink jet printers with individual jets or jets arranged in a matrix, which generate punctiform recording spots, operate along the same principle. The individual recording spots are recorded in correspondence with the grid which is dependent upon the recording frequency. In all of these cases, contours running diagonally to the recording direction are reproduced with poor quality, i.e. present a more or less stepped formation. An example of a general system of the type involved, and of stepped configurations is illustrated in German Offenlegungsschrift No. 2,639,856. This could of course be improved by a finer resolution, i.e. increasing the scanning and recording frequency or, effecting a refinement of the scanning and recording grid. This, however, will be associated with a greater cost and, if the recording apparatus will not permit a higher point frequency, with an impairment of the recording. In some of the aforementioned recording methods, this is only possible to a certain degree, as it is not possible to reduce the point size in the recording as greatly as would be desired.
A method as heretofore been proposed for effecting an improvement in the contour without increasing the fineness of the scanning or the scanning frequency. However, this improvement is effected on the first or leading edge occurring in the recording direction but not on the trailing edge. This method has been termed the "fractional step method" and makes it possible, with the same recording frequency, to displace the first point on an edge by a fractional pitch of the screen line distance in the direction of the contour. The subsequently following points are then written with the normal recording frequency which, however, result in the contour being reproduced at its trailing edge in the original stepped formation, i.e. the improvement thus occurred only along the leading edge of the contour.